Production of refractory platinumgroup metal spheroidal articles



Sept. 9, 1969 o. w. RHYS ETAL 3,466,165

PRODUCTION OF REFRACTORY PLATINUM-GROUP METAL SPHEROIDAL ARTICLES Filed Feb. 2, 1967 6040 1/56/77 PEXCEVVZ' mam My y Z3 2% ww W5 mi United States Patent US. Cl. 75-5 Claims ABSTRACT OF THE DISCLOSURE Small spheres and spheroid-like articles which are predominantly of ruthenium, iridium, osmium or rhodium are formed in a molten matrix of other metal and thereafter the matrix is solidified and leached away so as to recover the spheres or spheroidal articles.

The present invention relates to metallurgy of precious metals and, more particularly, to production of small article comprising ruthenium, iridium, osmium or rhodium.

Attempts have been made to provide small spheroidal articles of corrosion resistant metals. Small spheres and spheroids of metal offering high crush strength and good resistance to corrosion are of importance in many industrial applications, especially in the manufacture of pivots for the moving elements of compasses and other similar instruments. They are also useful in the manufacture of sintered porous metal filters. The manufacture of small spheres and spheroids for such has proved to be difiicult.

Although many attempts were made to overcome difliculties and disadvantages in production of small corrosion-resistant spheroidal articles, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It is an object of the present invention to provide a new process for forming substantially spherical articles, including spheroids and spheroid-like articles, of metals that comprise a high proportion of ruthenium, iridium, osmium or rhodium.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing which relates to the metallurgical ternary system of ruthenium, palladium and gold at 1200 C.

Generally speaking, the present invention contemplates a process wherein small substantially spherical articles of alloys of one of the corrosion-resistant refractory metals ruthenium, iridium, osmium or rhodium are made by taking one of these metals in the form of fine powder and subjecting the powder to contacting presence of a molten alloy comprising palladium or platinum and a second metal component which can be gold or silver, at a temperature below the melting point of the ruthenium, iridium, osmium or rhodium, allowing the whole to cool to form a solid matrix and leaching out the matrix. EX- cept where rhodium is employed, the second component of the matrix may be copper in place of all or part the gold or silver. While in contact with the molten alloy that forms the matrix the powdered ruthenium, iridium, osmium or rhodium is surprisingly converted into spheres and/or other substantially spherical articles and these are left when the matrix is removed. In the present process, the molten matrix has very low solubility and ditfusibility with the refractory metal, i.e., the ruthenium, iridium,

3,456,165 Patented Sept. 9, 1969 lCC osmium or rhodium, and the resulting refractory metal articles, although becoming slightly alloyed with the matrix metal during the process, are composed predominantly of the refractory metal.

In carrying the invention into practice it is advantageous to mix the powder of the refractory metal with the matrix metals, i.e., the palladium or platinum and the gold, silver or copper, which are also in powder form, compact the mixture and then beat the compact. The temperature for heating in such a process can be from 1000 C. to 1600 C. and is advantageously in the range 1450 C. to 1550 C.

Alternatively, the powder of the refractory metal can be compacted by itself under pressure, with or without sintering, and subsequently infiltrated with an alloy of palladium or platinum with gold or silver or copper. If the compact is sintered, it is advantageous to sinter it at a temperature of 800 C. to 1600 C. and then to effect the infiltration at a temperature at which the matrix alloy melts but at which the refractory metal powder in the compact does not melt.

Combinations of two or three of the metals gold, silver and copper can be employed in the molten alloy for the present process. However, combinations of palladium and platinum together should not be used in practicing the invention.

Powders of ruthenium, iridium, osmium or rhodium for the process of the invention are desirably in the size range of about 1 to about microns. Platinum, palladium, gold, silver or copper for the process can be in the form of commercially available powders.

While the matrix is molten the geometrical form of the final ruthenium or rhodium or iridium or osmium alloy articles is fashioned. The length of time of the sintering, the sintering temperature, the thermal cycling during sintering and the amount of ruthenium, rhodium, iridium or osmium in the combined alloys alfect the size to which the powder particles grow and consequently provide means for the control of the size of the spherical and spheroidal articles which are to be produced. The resulting spheroidal shapes are caused by contact of the liquid phase with the refractory metal. The leaching of the matrix of the alloy to free the spheres and spheroids is preferably efiected in aqua regia.

The process does not enable spheres and spheroids of absolutely pure ruthenium, iridium, osmium or rhodium to be produced since some, but very little, diffusion of the matrix metals with the powders of ruthenium, iridium, osmium or rhodium does occur. The overall proportions and properties of the metals are so chosen that alloys rich in ruthenium, iridium, osmium or rhodium will result from the process.

The very limited, low, mutual solubility and diffusivity characteristics of refractory metals and matrix alloys in accordance with the invention will now be illustrated further with reference specifically to the system rutheniumpalladium-gold.

Researches we have made have shown that in the ternary diagrams of the elements in question a line can be drawn as the boundary between single-phase and twophase alloys. The position of this line is dependent upon temperature and the accompanying drawing shows the ternary diagram of the ruthenium-palladium-gold system at 1200 C. The hatched area is that in which the system is single-phase and the plain area is substantially that in which the system has two or more phases, part of which can be liquid; line D shows a boundary between singlephase and two-phase alloys and on this line the compositions are those of the terminal solid solutions. The boundary line D is curved over part of its length and merges into the ruthenium and palladium axis of the diagram at about 25% ruthenium and about 60% palladium, respectively. Alloy or phase compositional percentages set forth herein are by weight unless expressly indicated otherwise, e.g., as atomic equivalents (atom-for-atom equivalents). To ascertain the exact shape of the curve in any ternary system involves much detailed work, but the curve shown herein is believed essentially correct.

In any two-phase alloy in a ternary system the two phases will be those of two terminal solid solutions and these will not diffuse into one another. A line joining the points in the ternary diagram that represent the compositions of these terminal solid solutions is called a tie line and in the system ruthenium-palladium-gold the tie lines run roughly in the direction of the line BC shown in the drawing.

In any two-phase alloy it is possible to determine the compositions of the two phases in it by an electron probe micro-analyzer or by other means. An alloy containing, for example, 30% gold, 20% ruthenium and 50% palladium, and therefore at the point A (where the 30% gold, 20% ruthenium and 50% palladium lines intersect) in the drawing, is found by the electron probe to contain two phases, the refractory metal-rich phase composition being substantially pure ruthenium and the matrix metal-rich phase composition being 62% palladium and 37% gold, 1% ruthenium. An alloy of the composition ruthenium lies on line D at point B, and an alloy of the composition 62% palladium and 37% gold, 1% ruthenium lies on the boundary line at point C. A line joining the points A, B and C is the tie line of the phases.

Thus if a mixture of powders of 30% gold, 20% ruthenium and 50% palladium that has been compacted and liquid-phase sintered or liquid-phase infiltrated is heated at 1200" C., there is obtained a two phase alloy, one phase of which consists of essentially pure ruthenium and the other of which consists of 62% palladium and 37% gold, 1% ruthenium the second of these is the matrix alloy. If the matrix alloy is then leached out and the other phase, of ruthenium, is recovered, this ruthenium-rich phase is surprisingly found to be in the form of small spheres or spheroids.

It is not in fact absolutely necessary to determine the composition of more than one phase in a two-phase alloy in order to draw any tie line, since a straight line will invariably pass through the points representing the twophase alloy itself and the two component phases. If one phase is ascertained, the other phase will therefore be of the composition at the point where the opposite end of the tie line intersects the boundary line. Once a tie line is established a pair of terminal solid solutions will be obtained by the use of any ternary composition on that tie line. Thus ternary metal compositions for the present process are ternary compositions that are on tie lines in two phase areas of ternary metallurgical systems having (where the system is represented by a triangular, threecoordinate diagram) at one apex a refractory metal from the group ruthenium, iridium, osmium and rhodium, at a second apex a metal from the group platinum and palladium and at the third apex a metal from the group gold, silver and copper with the exception that systems comprising both rhodium and copper in combination are not included. In addition, compositions in quaternary or quinary systems containing mixtures of gold, silver and copper but not mixtures of copper and rhodium can also be utilized. In accordance with the invention the metallurgical systems employed each have a matrix metal-rich phase which melts at temperatures lower than required for melting the accompanying refractory metal-rich phase.

For any ternary system in which the tie lines are not known those skilled in the art can determine, by known metallurgical techniques, how the tie lines lie on the ternary diagram. Once this is known, it is possible to provide an overall composition for the mixture of powders, which, when heated, will yield spheres or spheroids according to the invention composed of an alloy which is predominantly ruthenium, iridium, osmium or rhodium, with only a small proportion of other metal.

Spheres and other substantially spherical articles according to the invention can be formed by heating together mixtures of metals, wherein the matrix metals can be alloyed metals, consisting essentially of at least about 20% of only one metal from the refractory metal group ruthenium, iridium, osmium and rhodium, at least about 5% ofonly one metal from the first matrix metal group platinum and palladium, provided that when platinum is employed the amount thereof does not exceed about 10% and that when palladium is employed the amount thereof does not exceed about 60%, with the balance being metal from the second matrix metal group gold, silver, copper and mixtures thereof, provided that copper is not included when the refractory metal is rhodium and that metal of said second matrix metal group is present in a proportion which is atomically equivalent to at least about 5 weight percent gold and not more than about 60 weight percent gold when the alloy contains palladium and not more than about 70 gold when the alloy contains platinum. These ranges of composition are shown on the accompanying drawing by the areas STUVWS and SXYZS. Thus, a metal mixture for the process can comprise 5% to 70% gold, or in such a mixture the gold can be replaced by silver in atomically equivalent proportions. Also, except when rhodium is the refractory metal the gold can be replaced by atomically equivalent proportions of copper.

The process of the invention produces corrosion-resistant spheroidal articles which are of sizes ranging from about 50 microns up to about 200 microns, or even higher, in average diameter. In order to produce satisfactorily spheroidal articles of these sizes, the metal mixture for the process must be held with the matrix molten for at least about 5 minutes when starting sizes of the refractory metal powders are up to about 20-30 microns. Advantageously, for obtaining nearly spherical articles of desirably large sizes of at least about 10200 microns in diameter the mixture is held with the matrix molten for a period of at least about 30 hours.

For the purpose of giving those skilled in the art a better understanding of the invention and a better appreciation of the advantages of the invention, the following illustrative examples are given.

EXAMPLE I A mixture of metal powders comprising about 30% ruthenium metal powder of about 0.25 micron size, about 35% gold metal powder of about 4 microns size and about 35% palladium metal powder of about 10 microns size is compacted and then heated at a temperature of about 1500 C., for about 4 hours. Thereafter the mixture is cooled to room temperature and leached with aqua regia. After the leaching, spheroids composed predominantly of the refractory metal ruthenium and having diameters of about 30 microns are recovered.

EXAMPLE II Ruthenium metal powder of an average particle size of about 0.25 micron is compacted and then infiltrated with a molten alloy consisting essentially of about 50% gold and about 50% palladium. The resultant combined mixture of refractory metal and matrix metal comprises about 20% ruthenium, about 40% gold and about 40% palladium. The infiltrated compact is held at a temperature of about 1500 C. for about 28 hours. After the infiltrated compact is cooled, the matrix alloy, which is comprised predominantly of the alloy employed for infiltration, is leached with aqua regia and substantially spherical articles composed predominantly of ruthenium and having average diameters of about microns are recovered.

The small spheroidal articles, e.g., spherules, produced in accordance with the invention are predominantly of the especially hard, high melting point, platinum-group metals referred to herein as refractory metals. These articles have high crush strength and corrosion resistance and are generally useful in bearing applications where these characteristics are needed.

The present invention is particularly applicable to production of small corrosion resistant articles for use as tips on fountain pen nibs and as pivots for moving elements of compasses and other similar instruments. The articles are also suitable for sintered porous metal filters.

Although the present invention has been described in conjunction with the preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A process for making small refractory platinumgroup metal spheroidal articles comprising subjecting particles of metal powder consisting essentially of one metal from the refractory metal group ruthenium, iridium, osmium and rhodium to contacting presence with a molten alloy consisting essentially of one metal from a first matrix metal group consisting of palladium and platinum and metal from a second matrix metal group consisting of gold, silver, copper and mixtures thereof provided that copper is not included when the refractory metal is rhodium, said refractory metal and matrix metals being present in proportions of a two-phase alloy comprising a refractory metal-rich phase and a matrix metal-rich phase, said matrix metal-rich phase being characterized by being meltable at a temperature lower than required for melting the refractory metal phase, maintaining the matrix metal alloy molten while retaining said refractory metal powder in a solid condition to convert said powder to spheroidal articles composed predominantly of the refractory metal, thereafter solidifying the molten matrix, removing the matrix from the spheroidal articles and recovering said spheroidal articles composed predominantly of the refractory metal.

2. A process as set forth in claim 1 wherein the matrix alloy is maintained molten for a period sufficiently long to form spheroidal articles of sizes greater than the starting particle sizes of the refractory metal powder.

3. A process as set forth in claim 1 wherein the matrix is removed by leaching.

4. A process as set forth in claim 1 wherein the total of the combination of refractory metal and matrix metals includes at least 20% of the refractory metal, at least 5% of metal from the first matrix metal group provided that palladium is not present in an amount exceeding and that platinum is not present in an amount exceeding 10% and wherein metal from the second matrix metal group is present in a proportion atomically equivalent to at least about 5 weight percent gold and not more than about 60 weight percent gold where the first matrix metal is palladium and not more than about weight percent gold where the first matrix metal is platinum.

5. A process as set forth in claim 1 wherein there is provided a mixture of solid metal powders consisting essentially of one metal from the refractory metal group, one metal from the first matrix metal group and metal from the second matrix metal group, wherein the mixture is heated to provide a molten matrix metal alloy composed predominantly of the matrix metals while retaining the refractory metal powder in a solid condition and wherein the matrix is maintained molten to form the refractory metal powder into spheroidal articles.

6. A process as set forth in claim 5 wherein the powder mixture is heated to a temperature of about 1000 C. to about 1600" C.

7. A process as set forth in claim 5 wherein the metal powders in the mixture are of elemental metals.

8. A- process as set forth in claim 5 wherein the powder metal mixture includes elemental powder of the refractory metal and alloy powder of one metal from the first matrix metal group and of metal from the second matrix metal group.

9. A process as set forth in claim 1 wherein the refractory metal powder is compacted and is then infiltrated with the molten alloy of the matrix metals.

10. A process as set forth in claim 9 wherein the infiltration is performed with the refractory metal and matrix metals at a temperature of about 800 C. to about 1600 C.

References Cited UNITED STATES PATENTS 2,384,501 9/1945 Streicher 0.5 3,019,485 2/l962 Diamond 264-15 L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 2645, l5

mg? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 3, 5 Dated May 1, 1970 I r) DAVID WADE RHYS, PETER EDWARD GAINSBURY and RONALD SAVAG It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I" Column line 38, for "1o 20o" read -lOO-200--. .1

SIGNED AND SEALED AUG 4 -19?!) fir-2:! (SEAL) Afloat:

EdwardMHeteher,Ir. I-HM! I. JR. A 0mm comissioner o1 Patents 

